Organization of cells in the inner ear enables the sense and sensitivity of hearing

May 14, 2018, Massachusetts Eye and Ear Infirmary
Depiction of the inner ear, with a stylized glimpse inside at the vibrating lattice of 'Y-shaped' cellular architecture found within the organ of Corti. Credit: Hamid Motallebzadeh, Garyfallia Pagonis, Peter Gottlieb, Haobing Wang, and Sunil Puria of Mass. Eye and Ear

The loss of tiny cells in the inner ear, known as "hair cells," is a leading cause of hearing loss, a public health problem affecting at least one out of three people over the age of 65. Of the two varieties of hair cells, the "outer hair cells" act as micromotors that amplify incoming sound, and the "inner hair cells" act to sense and transmit information about the sound to the brain. Hair cells do not regenerate on their own in human ears, and they can die away from a variety of factors including excessive noise exposure, certain medications, infection and as part of the natural aging process.

Researchers around the world are working to restore human hearing by regenerating outer in the cochlea of the inner ear, the loss of which is a leading cause of hearing impairment, through a variety of techniques, and some have even shown success in restoring some hearing sensitivity in animal studies. However, new research shows that restoring hearing is not just about regenerating the lost outer hair cells. In a study published online today in the journal Proceedings of the National Academy of Sciences (PNAS), a research team from Mass. Eye and Ear has shown that, in order to effectively amplify and tune sound, each of the outer hair cells must be arranged as a specific branch of a Y-shaped building block, which is replicated thousands of times within the cochlea to form a highly organized cellular architecture.

"Our work suggests that, in order for humans to hear well, the outer hair cells in the cochlea not only need to be in good working order, but also need to be connected to other nearby cochlear structures in a very particular way," said senior author Sunil Puria, Ph.D., an Amelia Peabody Scientist at Mass. Eye and Ear and instructor in otolaryngology at Harvard Medical School. "It had been assumed that, if we could just succeed in regenerating outer hair cells, it would be sufficient to restore hearing. But our work shows that the spatial organization of the restored cells must also be taken into account."

Motivated by previous studies in their lab, the researchers created a detailed computer simulation of the cochlea and the tiny structures within it. They then tested how different arrangements and malformations of the Y-shaped structures affect hearing function. They found that the outer hair cells could only produce high hearing sensitivity and frequency selectivity when arranged in their natural configuration with respect to the surrounding structures. When they altered the geometry and material properties of these structures, the cells' ability to amplify and tune sound was compromised.

The study provides an important step toward understanding the functional implications of how the are arranged in the inner ear—with far-reaching implications for emerging new clinical therapies that aim to restore by regenerating these cells, but not necessarily in a way that restores their critical position within the natural Y-shaped building blocks of the cochlea.

"We built our model to test whether rearranging the cells in the Y-shaped structures of the inner ear alters the ear's ability to amplify sound," said Dr. Puria. "By altering these structures in the model, we see strong evidence that amplification and tuning in the cochlea depend heavily on the natural arrangement of these structures."

According to co-author Hamid Motallebzadeh, Ph.D., a postdoctoral fellow at Mass. Eye and Ear, "Computational models such as the one developed for this study can be used to replicate and interpret experimental measurements, thus potentially reducing the need for animal-based studies, and can also allow researchers to conduct well-controlled 'virtual experiments' that go far beyond what is currently possible to perform in actual experiments."

Explore further: Simple treatment may minimize hearing loss triggered by loud noises

More information: Hamid Motallebzadeh el al., "Cochlear amplification and tuning depend on the cellular arrangement within the organ of Corti," PNAS (2018). www.pnas.org/cgi/doi/10.1073/pnas.1720979115

Related Stories

Simple treatment may minimize hearing loss triggered by loud noises

May 7, 2018
It's well known that exposure to extremely loud noises—whether it's an explosion, a firecracker or even a concert—can lead to permanent hearing loss. But knowing how to treat noise-induced hearing loss, which affects ...

Researchers discover how the brain balances hearing between our ears

May 12, 2015
UNSW researchers have answered the longstanding question of how the brain balances hearing between our ears, which is essential for localising sound, hearing in noisy conditions and for protection from noise damage.

Sensory hair cells regenerated, hearing restored in mammal ear

January 9, 2013
Hearing loss is a significant public health problem affecting close to 50 million people in the United States alone. Sensorineural hearing loss is the most common form and is caused by the loss of sensory hair cells in the ...

New technique generates high volume of sensory cells needed for hearing

February 21, 2017
The loss of tiny, sound-sensing cells in the inner ear, known as "hair cells," is a leading cause of hearing loss, a public health problem affecting at least 5 percent of the world population. Hair cells, which do not regenerate ...

Researcher describes cochlear amplification using novel optical technique

December 12, 2012
It has long been known that the inner ear actively amplifies sounds it receives, and that this amplification can be attributed to forces generated by outer hair cells in the cochlea.  How the ear actually accomplishes this, ...

New images reveal how the ear's sensory hairs take shape

February 9, 2018
Our ears are exquisite detection instruments, capable of discerning a whisper or distinct notes of music within a symphony. To pick up these sounds, tiny hair-like filaments in the inner ear must be packed into precisely ...

Recommended for you

3-D bioPen: A hydrogel injection to regenerate cartilage

September 25, 2018
Highly specialized cartilage is characteristically avascular and non-neural in composition with low cell numbers in an aliphatic environment. Despite its apparent simplicity, bioengineering regenerative hyaline cartilage ...

Skin wounds in older mice are less likely to scar

September 25, 2018
Researchers have discovered a rare example in which the mammalian body functions better in old age. A team at the University of Pennsylvania found that, in skin wounds in mice, being older increased tissue regeneration and ...

Extracellular RNA in urine may provide useful biomarkers for muscular dystrophy

September 25, 2018
Massachusetts General Hospital (MGH) researchers have found that extracellular RNA (exRNA) in urine may be a source of biomarkers for the two most common forms of muscular dystrophy, noninvasively providing information about ...

Evidence that addictive behaviors have strong links with ancient retroviral infection

September 24, 2018
New research from an international team led by Oxford University's Department of Zoology and the National-Kapodistrian University of Athens, published today in Proceedings of the National Academy of Sciences (PNAS), shows ...

Taking a catnap? Mouse mutation shown to increase need for sleep

September 24, 2018
Sleep is vital for adequate functioning across the animal kingdom, but little is known about the physiological mechanisms that regulate it, or the reasons for natural variation in people's sleep patterns.

Know someone sick? Your own smell might give it away

September 24, 2018
Odors surround us, providing cues about many aspects of personal identity, including health status. Now, research from the Monell Center extends the scope and significance of personal odors as a source of information about ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.